1. Field of the Invention
The present invention relates in general to a fluid-filled elastic mount adapted to provide a vibration damping effect based on fluid flows through an orifice passage. More particularly, the present invention is concerned with such a fluid-filled elastic mount having a rotary valve operated to control fluid communication of orifice passage or passages with fluid chambers, to thereby change damping characteristics of the elastic mount.
2. Discussion of the Prior Art
There is well known a fluid-filled elastic mount as disclosed in JP-A-60-104824, which is connected to and interposed between two members of a vibration system such that these two members are elastically connected to each other, or such that one of these two member is supported by the other member in a vibration damping fashion. Such a fluid-filled elastic mount comprises (a) a first mounting member to be attached to one of the two members of the vibration system, (b) a generally cylindrical second mounting member to be attached to the other of the two members of the vibration system, the second mounting member including a cylindrical wall, (c) an elastic body elastically connecting the first and second mounting members so as to fluid-tightly close one of axially opposite open ends of the second mounting member, (d) a flexible diaphragm which fluid-tightly closes the other open end of the second mounting member, and which cooperates with the elastic body and the second mounting member to define a fluid-tight space, (e) a partition member disposed in the fluid-tight space so as to divide the fluid-tight space into a pressure-receiving chamber which is partially defined by the elastic body and filled with a non-compressible fluid and whose pressure changes upon application of a vibrational load to the elastic mount, and an equilibrium chamber which is partially defined by the flexible diaphragm and filled with the non-compressible fluid and whose volume is variable by displacement of the flexible diaphragm, (f) means for defining at least one orifice passage for fluid communication between the pressure-receiving chamber and the equilibrium chamber. This type of fluid-filled elastic mount is capable of exhibiting high damping effects based on resonance of the fluid flows through the orifice passage, which effects cannot be provided by an elastic mount which does not utilize fluid flows through an orifice passage. For example, the fluid-filled elastic mount is suitably used as an engine mount for an automotive vehicle.
Generally, a fluid-filled elastic mount such as a vehicle engine mount is required to be able to damp vibrations having different frequencies and amplitudes. However, the range of frequency of the input vibrations that can be effectively damped by fluid flows through an orifice passage is narrower than the frequency range of the input vibrations. Therefore, a fluid-filled elastic mount using a single orifice passage is not generally capable of exhibiting desired damping characteristics for dealing with the input vibrations. In view of this tendency, JP-U-4-122841 (laid-open publication of Japanese Utility Model Application) proposes a fluid-filled engine mount which has a first orifice passage, a second orifice passage tuned to damp vibrations whose frequencies are higher than those of the vibrations that can be damped by the first orifice passage, and a third orifice passage tuned to damp vibrations whose frequencies are higher than those of the vibrations that can be damped by the second orifice passage. A flexible rubber layer or film is disposed in the third orifice passage such that the rubber layer undergoes elastic deformation and permits fluid flows in the third orifice passage upon application of high-frequency vibrations, and restricts the fluid flows in the third orifice passage upon application of low-frequency vibrations. The proposed engine mount includes a rotary valve which is supported by the partition member such that the rotary valve is rotatable about an axis substantially perpendicular to the axis of the generally cylindrical second mounting member. The second and third orifice passages are open on a sliding surface of the partition member on which the rotary valve is slidably rotated, so that the second and third orifice passages are selectively closed and opened, namely, selectively brought into communication with the equilibrium chamber when the rotary valve is rotated between two positions corresponding to the second and third orifice passages. Thus, the proposed engine mount exhibits different damping characteristics with selective functioning of the three orifice passages.
In such known engine mount, a drive shaft of the rotary valve which receives a torque from an external actuator projects outwardly of the engine mount, extending through the partition member and the second mounting member. The drive shaft is connected at its outer end to the external actuator, so that the rotary valve is rotated by the actuator through the drive shaft. Generally, a linear actuator of pneumatic diaphragm type adapted to generate a reciprocating or linear movement is suitably used for the engine mount, since it is simple in construction and since a vacuum source is usually provided on a motor vehicle with an internal combustion engine.
Such linear actuator requires a motion converting mechanism including a link member for converting a reciprocating movement into a rotary movement of the rotary valve. That is, the output shaft of the linear actuator should be connected to the rotary drive shaft of the rotary valve through the link member. The link member is connected at its one end to the rotary drive shaft which projects from the housing of the engine mount, and the output shaft of the linear actuator is connected to the other end of the link member. Accordingly, the converting mechanism uses a relatively large number of components for connecting the drive shaft of the linear actuator to the rotary drive shaft of the rotary valve, and the assembling of the actuator with the engine mount tends to be cumbersome. Further, the drive shaft of the rotary valve inevitably projects a considerable distance from the engine mount, and the link member and the output shaft of the linear actuator are required to be spaced a considerably large distance away from the housing of the engine mount. In addition, the movement of the link member requires a large space between the linear actuator and the engine mount. Thus, the engine mount equipped with the linear actuator tends to be large-sized and requires a considerably large space for installation on the vehicle.